Effect of Fe substitution on the structure and magnetocaloric effect of Mn_5−xFe_xGeSi₂ alloys

The structure and magnetocaloric effect of Mn_5−xFe_xGeSi₂ compounds were studied. Analysis of X-ray powder diffraction and energy dispersive X-Ray spectroscopy revealed that Mn_5−xFe_xGeSi₂ alloys with x<1 crystallize in the Mn₅Si₃-type structure (space group P6₃/mcm), maintaining the structure of Mn₅Ge₃; and alloys with x=1.5 and 2 consist of the major Mn₅Si₃-type phase and the minor Ni₂In-type phase (space group P6₃/mmc). The results of Rietveld refinement showed that the cell parameters for the Mn₅Si₃-type phase decrease with increasing Fe content. The positive slopes in Arrott plots indicate that a second-order ferromagnetic to paramagnetic transition occurs. The Curie temperature increases with increasing Fe content from 182 K for x=0.6 to 224 K for x=2. The maximum magnetic entropy change of 3.7 J/(kg K) for x=0.8 was found under a magnetic field change of 0–20 kOe. - Highlights: • Mn_5−xFe_xGeSi₂ alloys with x<1 crystallize in the hexagonal Mn₅Si₃-type structure. Alloys with x=1.5 and 2 consist of a major Mn₅Si₃-type phase and a secondary Ni₂In-type phase. • The cell parameters decrease and the Curie temperature increases with increasing x in Mn_5−xFe_xGeSi₂ alloys. • The maximum -∆S_M of 3.7 J/(kg K) and RCP of 211 J/kg for x=0.8 was found under a magnetic field change of 0–20 kOe.